kierendavies

# This program solves a puzzle I encountered recently.
# The puzzle consists of four cubes, each face of which has one of four colours.
# The objective is to arrange them in a column so that, looking down each side
# of the column, the four visible colours are all different.

require 'pp'
require 'set'

# A cube with colours attributed to its faces.
class Cube

kierendavies

; Burrows-Wheeler Transform (and inverse)
; http://en.wikipedia.org/wiki/Burrows%E2%80%93Wheeler_transform

(def string-start \u0098)

(defn bwt [s]
  (map last
       (sort-by vec
                (take (inc (count s))
                      (iterate #(concat (rest %)